The present invention generally relates to head loading mechanisms for a flexible (floppy) disc drive unit, and in particular to a head loading mechanism for bringing into contact and withdrawing a magnetic read/write head with and from a flexible magnetic disc.
Currently, a flexible disc drive unit (hereafter simply referred to as an FDD unit) is widely used as a data storage means. A flexible magnetic disc which is generally rotatably housed in a square and apertured jacket is inserted into the FDD unit through an entrance slot in the front thereof at the time of its use. The inserted magnetic disc is located and held on a spindle by a magnetic disc loading arm. The magnetic disc can be rotated by a spindle motor coupled with the spindle. A pair of magnetic read/write heads which are mounted on a magnetic head carriage are linearly transported and set over and under instructed track positions formed on storage surfaces of the magnetic disc by a carriage transporting mechanism. Thereafter, the magnetic heads are brought in contact with the disc surfaces by a head loading mechanism.
The head loading mechanism includes a head load bail which is rotatably supported and which may come in contact with a magnetic head loading arm of the head carriage. The head loading arm has one of the two heads and is urged by a spring so that it is withdrawn from the magnetic disc When the read/write operation is instructed, the head loading arm is rotatably moved against the spring force by the bail so that the magnetic head attached to the head loading arm approaches and makes contact with the disc storage surface. During the read/write operation, the magnetic head is kept in contact with the disc storage surface This state is called a head load state, and an operation to obtain the head load state is called a head loading operation. In the head load state, the magnetic disc is brought and kept in contact with the other magnetic head secured to a part of the head carriage opposite to the head loading arm. During the read/write operation, the bail disengages and is held away from the head loading arm.
When the desired read/write operation is completed, the bail is de-activated and rotates in the reverse direction. At this time, the bail comes in contact with the head loading arm again so that the magnetic head of the head loading arm is withdrawn from the disc surface. Then, the bail is brought into contact with the disc loading arm and is stopped thereby. As a result, the magnetic head of the head loading arm is held away from the magnetic disc. This state is called a head unload state and an operation to obtain this state is called a head unloading operation. Simultaneously, the magnetic head mounted on the part opposite to the head loading arm is separated from the magnetic disc.
In general, the bail is rotatably driven by an electromagnetic driving apparatus such as a plunger solenoid unit, which is disclosed in Japanese Laid-Open Patent Application No. 90471/1981, for example.
In the FDD unit, the head loading operation and the head unloading operation are frequently repeated Therefore, various problems described below may occur at the time of loading or unloading the magnetic head.
A position of the head loading arm in the head unload state is an important factor for obtaining smooth landing of the magnetic head secured to the head loading arm. In the head unload state, a gap must be formed between the magnetic head and the magnetic disc clamped on the spindle. The width of this gap is defined by the position of the head loading arm in the head unload state. In addition, the following fact is also an important factor for obtaining smooth lifting of the magnetic head. In the head load state, the bail is held away from the head loading arm. In other words, a gap is formed therebetween. If this gap is large, at the time of unloading the magnetic head, the bail strikes the head loading arm excessively strongly, so that the head loading arm is undesirably vibrated. The gap between the bail and the head loading arm is defined by a position of the bail in the head load state. In general, the bail is designed to make contact with the head loading arm by a finger which is a part of the head loading arm.
However, the conventional head loading mechanism does not have any effective mechanism for adjusting the gap between the magnetic head secured to the head loading arm and the magnetic disc held on the spindle. When taking into consideration an error at the time of assembling the mechanism, it is difficult to obtain the gap narrower than 0.5 mm. This value of the gap is insufficient to obtain the smooth landing of the magnetic head. In other words, the magnetic head strikes the disc excessively strongly at the time of loading the head. This distorts a signal waveform of an output of the magnetic head, and elongates a time spent until the head output is stabilized after the start of the head loading operation. Of course, it is impossible to write and read data on and from the magnetic disc during a unstable state of the head output. This prevents the speedy read/write operation.
The conventional head loading mechanism is also not provided with any effective mechanism for adjusting the position of the bail in the head load state, in other words, the gap between the bail and the finger part of the head loading arm. When taking into consideration an error at the time of assembling the mechanism, it is difficult to reduce the gap to smaller than 1 mm, which is not a satisfactory value for the bail to smoothly lift the magnetic head. That is, the head loading arm is strongly hit by the bail. Thereby, the magnetic head attached to the head loading arm is undesirably vibrated on the magnetic disc so as to repeatedly engage with and disengage from the magnetic disc This distorts the envelope of the output signal, so that a long time is taken until the head output becomes absolutely zero after the start of the head unloading operation. Furthermore, the above fact may cause damage to the magnetic disc and the magnetic head.